Metal abrasive sheet and a method of making same



Aug. 27, 1968 A. o. PALMER 3,393,442

METAL ABRASIVE SHEET AND A METHOD 0F MAKING SAME Filed March 4, 1965 FIGJ INVENTOR ALBERT O. PALMER BY W415. mm

ATTORNEY United States Patent 3,398,442 METAL ABRASIVE SHEET AND A METHOD OF MAKING SAME Albert 0. Palmer, Ridgefield, Conn., assignor to Gar Precision Products, Inc., Danbury, Conn., a corporation of Connecticut Filed Mar. 4, 1965, Ser. No. 437,062 Claims. (Cl. 29-78) The invention relates to a metal abrasive sheet. The conventional sandpaper employed for smoothing the surfaces of articles has the disadvantage that it constantly breaks down from an original to a smaller grit thus reducing its effective use by slowing the cutting action and losing its effectiveness, entirely after a relatively very short time of use.

The invention aims therefore to provide and produce an abrasive sheet of a very much greater wear resistance than sandpaper and which can be produced in all standard grit sizes to meet allthe requirements hitherto met by sandpaper for rough sanding to final finishing and which may be used on wood, soft metals or plastics, either wet or dry.

It is another object of the invention to produce a metal abrasive sheet whereby all grit sizes of sandpaper can be exactly duplicated and replaced and wherein the grit is integral with the base sheet, which is contrary to sandpaper wherein the sand and the basic paper are heterogeneous materials jointed together by some adhesive means.

Still another object of the invention is the production of a metal abrasive sheet by electroforming wherein the sheet may be of any desired thickness and the grit of any desired standard size.

The invention further aims to use a sandpaper of a desired grit size as a matrix from which a negative will be taken to serve as a master for electroforming positive metal abrasive sheets, preferably of nickel.

In a process according to the invention, I take a sheet of sandpaper of desired grit size and mount it properly against a backing plate to provide a smooth working surface. The backing plate may be wood, fiberglass, metal or any other material capable of withstanding the temperature which may be applied in the course of the process. Any suitable adhesive may be employed for attaching the sandpaper to the backing plate. I found the use of a pressure sensitive double-faced tape adequate. From the top face of the sandpaper a negative copy is extracted in a semi-rigid material, such as silicone rubber, rubber, polyvinylchloride, or other suitable material. I prefer to use polyvinylchloride which is poured in liquid state over the surface to be copied. It is retained in a simple frame which restrains the liquid and simultaneously determines the thickness of the final negative. In the event the proposed polyvinylchloride is used the entire assemblage of sandpaper, backing plate, frame and polyvinylchloride is placed in an oven and heated to 360 F. for about 30 minutes whereby the polyvinylchloride is cured to a material with properties similar to vulcanized rubber. The polyvinylchloride negative is then mechanically stripped from the sandpaper surface and attached with pressure sensitive double-faced tape to a suitable backing plate, for example, plexiglass. T hereby the flexible negative is held in the desired shape to serve as a master for the production of abrasive metal sheets by electroforming.

In the process of making an abrasive metal sheet from the master, the latter will first be sensitized e.g. by a stannous chloride solution whereupon a conductive metal is applied thereto in any conventional manner. For example, a surface of finely divided silver is obtained by spraying with amoniacal silver solution and a reducing agent, such as hydrazine. Onto this surface a metal, for

ice

example, nickel will be deposited by a conventional electroforming process. Thus, for a product of pure nickel, the electroforming may take place in 21 Watts bath or a nickelsulfamate bath of well-known composition. When a sufficient thickness has been deposited and since there is no molecularbond between the deposition and the substrate the electroformed metal can easily be mechanically separated from the semi-rigid master and now constitutes a positive abrasive metal sheet of a grit size and formation of projecting grit particles, an exact copy of the sandpaper from which the negative master was taken. This product may be marketed in various sheet and strip forms, and is interchangeable with conventional sandpaper in devices designed to hold sandpaper, both hand and power activated. A variation of this process to improve wearing qualities is the application of an initial electro-deposition of hard metal followed by a secondary application of a more ductile metal by electrodeposition, thus providing a hard wearing surface while still retaining the desirable flexible characteristics of conventional abrasive products. I prefer to use nickel as the hard as well as the ductile metal. Whereas the ductile nickel is electroformed in one of the above mentioned baths, preferably in a nckelsulfamate bath of conventional composition, the hard nickel layer is obtained from such a bath to which an organic agent, such as saccharin is added, as it is well known in the art.

The accompanying drawing illustrates by way of example the method of production of the product according to the invention. In the drawing,

FIG. 1 is a cross-section of a portion of the master, on an enlarged scale, in the process of its production;

FIG. 2 is a cross-section, also on an enlarged scale, of a portion of an electroformed sheet still on the master;

FIG. 3 is a top plan view of a portion of the abrasive metal sheet with a backing.

Referring now to the drawing, in FIG. 1 a piece of sandpaper 1 of desired grit size is mounted on a backing plate 2 e.g. of fiberglass by means of double-faced tape 3. A frame 5 is placed on the sandpaper and polyvinylchloride in liquid state is poured over the sandpaper in frame 5 which is of a height as desired for the thickness of the negative master. The assemblage of FIG. 1 will, then, be baked in an oven at about 360, as stated hereinbefore in order to cure the polyvinylchloride.

In FIG. 2 the cured polyvinylchloride 4, now constituting the master, is removed from the sandpaper 2 and attached by strips of double-faced tape to a backing plate 6. Reduced silver 7 is applied to the coarse surface whereupon a metal sheet 8, in the present case hard nickel, is electro-formed thereon and a reinforcing backing of ductile nickel 9 is formed onto the first deposit of hard nickel. The composite nickel sheet is then mechanically stripped from the master negative whereupon further abrasive sheets may be produced by using the same master.

FIG. 3 finally shows a portion of the produced nickel sheet 8 with its abrasive surface 8' and backing 9. This product has all the aforementioned valuable qualities.

It will be apparent to those skilled in the art that many modifications and alterations of the structure illustrated and described can be made without departure from the essence and spirit of the invention which for that reason shall not be limited but by the scope of the appended claims.

I claim:

1. The method of making an abrasive metal sheet comprising the steps of covering a sandpaper of desired grit size with a flexible matter so as to obtain a negative im print of the sandpaper grit on said flexible matter, electroforming a metal sheet on the so negatively gritted surface,

and stripping the so produced metal sheet from the last mentioned surface.

2. The method of making an abrasive metal sheet comprising the steps of covering a sheet of sandpaper of desired grit size with a flexible matter so as to obtain a negative imprint of the sandpaper grit on said flexible matter, electroforming a sheet of nickel on the so negatively gritted surface of said flexible matter and stripping the so produced abrasive nickel sheet from said surface.

3. A method according to claim 2 including electroforming a backing on said nickel sheet before stripping it from said surface of flexible matter.

4. A method according to claim 2 including electroforming said nickel sheet of hard nickel and electroforming thereon a backing of ductile nickel before stripping the so produced composite nickel sheet from said surface.

5. The method of making an abrasive metal sheet comprising the steps of covering a sheet of sandpaper, of desired grit size, with liquid polyvinylchloride, baking the assemblage of said sandpaper and polyvinylchloride in an oven at a temperature at which said polyvinylchloride gets cured to a layer having the sandpaper grit negatively imprinted in one surface of said layer, removing said layer from said sandpaper, electroforming a metal sheet on said gritted layer and removing said electroformed sheet from said polyvinylchloride.

6. The method of making an abrasive metal sheet comprising the steps of attaching a sheet of sandpaper with its grit of desired size exposed to a backing board, covering the exposed sandpaper side with liquid polyvinylchloride in a frame determining the thickness of the polyvinylchloride layer, baking the assemblage of said sandpaper, backing board, frame and polyvinylchloride in an oven at a temperature required to cure said polyvinylchloride to a flexible layer having the sandpaper 9 3,398,442 a. i-v

grit negatively imprinted on one of its surfaces, removing said layer from said sandpaper, attaching said layer with said gritted surface exposed to another backing board whereby said layer on said other backing board constitutes a negative master for an abrasive metal sheet to be electroformed thereon.

7. A method as claimed in claim 6 wherein said sandpaper and said layer of polyvinylchloride are being attached to the respective backing boards by means of double-faced tape.

8. A method according to claim 5, comprising the further steps of rendering said negative master conductive with reduced silver, electroforming a sheet of hard nickel on said silver in a nickelsulfamate bath, electroforming a ductile metal backing on said nickel sheet, and stripping said nickel sheet with ductile metal backing from said master.

9. A product produced by the method of claim 1.

10. A product produced by the method of claim 4.

References Cited UNITED STATES PATENTS 75,568 3 /1868 Nickerson 2978 349,490 9/ 1 886 Gallagher 2978 1,466,391 8/1923 Eskew et al 2978 1,875,346 9/ 1932 Laukel 204-281 FOREIGN PATENTS 461,478 11/ 1949 Canada. 535,623 1/ 1957 Canada.

JOHN H. MACK, Primary Examiner.

T. TUFARIELLO, Assistant Examiner. 

1. THE METHOD OF MAKING AN ABRASIVE METAL SHEET COMPRISING THE STEPS OF COVERING A SANDPAPER OF DESIRED GRIT SIZE WITH A FLEXIBLE MATTER SO AS TO OBTAIN A NEGATIVE IMPRINT OF THE SANDPAPER GRIT ON SAID FLEXIBLE MATTER, ELECTROFORMING A METAL SHEET ON THE SO NEGATIVELY GRITTED SURFACE, AND STRIPPING THE SO PRODUCED METAL SHEET FROM THE LAST MENITIONED SURFACE. 